Wetland bird population trends on Special Protection Areas (SPAs) in the UK were published today as WeBS Alerts Official Statistics.
The UK is host to internationally important numbers of wintering waterbirds, and the long-term monitoring by the JNCC/RSPB/BTO Wetland Bird Survey (WeBS) provides essential data that informs decision makers when considering conservation measures for these birds.
Protecting these internationally important numbers of non-breeding waterbirds is one of the reasons for designating SPAs in the UK. Every few years the status of these waterbird species is assessed by analysing WeBS data collected from within these SPAs and producing site-specific population trends covering the most recent 5 years, 10 years and 25 years, and since the original designation of the SPA. If these trends show a decline of 25 to 50% a Medium Alert is issued, and a decline of over 50% triggers a High Alert. These Alerts, which are published as Official Statistics, are intended to be advisory and are used as a basis on which to direct research and subsequent conservation efforts if required.
Population trends were assessed for site/species combinations on 87 SPAs for 45 species plus the overall waterbird assemblage, resulting in a total of 1,995 assessments across the four time periods. Of these, 39% triggered an Alert (404 High Alerts and 365 Medium Alerts), which is almost identical to the previous Alerts published in 2019 when 40% of assessments triggered an Alert.
Every SPA has 'qualifying features' – these are the specific bird species for which the site has been designated – and the number of assessed waterbird species that are qualifying features on SPAs vary. While there are only one or two on over one-third of the SPAs, ten or more feature species were assessed on 16 of the SPAs. The Firth of Forth SPA has the largest number (24) of assessed qualifying features. The number of Alerts triggered on an SPA is not proportionate to the number of waterbird features on the site. Similarly, some waterbird species feature in the designation of only one or two SPAs, while Redshank features most frequently, being a designating feature on 31 SPAs.
While no Alerts were issued for a small number of species, there were 20 occurrences across the four time periods where a species triggered an Alert in ten or more SPAs, with Dunlin triggering Alerts on 18 SPAs in the long-term assessments alone. Bewick’s Swan, a nationally declining species, triggered a High Alert since the baseline surveys on every one of the 16 SPAs where it is a designating feature.
The declines triggering the Alerts may be caused by site-specific pressures such as food availability, disturbance from human activities and habitat loss, or they may be caused by widespread pressures such as impact of climate change or one of many different pressures encountered by these species on their breeding grounds.
Site-specific detail that these headline WeBS Alerts have been drawn from can be explored via the interactive BTO Research Report 786 (Caulfield et al. 2025). These include interpretative notes on whether widespread pressures or site-specific pressures are likely to be the main driver on each site.
WeBS Alerts were funded by Natural England and the JNCC/RSPB/BTO WeBS partnership.
To find out more, visit the WeBS Alerts Official Statistics webpage.